Distinct expression profiles of Notch-1 protein in human solid tumors: Implications for development of targeted therapeutic monoclonal antibodies.

Biological therapies, such as monoclonal antibodies (mAbs) that target tumor-associated antigens have been considered an effective therapeutic approach in oncology. In considering Notch-1 receptor as a potential target, we performed immunohistochemistry on tissue microarrays to determine 1) whether the receptor is overexpressed in tumor cells as compared to their corresponding normal tissues and 2) the clinical significance of its expression levels in human breast, colorectal, lung and prostate cancers. We found that the expression of Notch-1 protein was overexpressed in primary colorectal adenocarcinoma and nonsmall cell lung carcinoma (NSCLC), but not in primary ductal breast carcinoma or prostate adenocarcinoma. Further analysis revealed that higher levels of Notch-1 protein expression were significantly associated with poorer differentiation of breast and prostate tumors. Strikingly, for NSCLC, the expression levels of Notch-1 protein were found to be inversely correlated with tumor differentiation and progression. For colorectal tumors, however, no correlation of Notch-1 protein expression was found with any tumor clinicopathological parameters, in spite of its overexpression in tumor cells. Our data demonstrated the complexity of Notch-1 protein expression in human solid tumors and further supported the notion that the roles of Notch-1 expression in tumorigenesis are highly context-dependent. The findings could provide the basis for development of distinct therapeutic strategies of Notch-1 mAbs for its applications in the treatment of suitable types of human cancers.

Choice of fixative is crucial to successful immunohistochemical detection of phosphoproteins in paraffin-embedded tumor tissues.

Protein phosphorylation is frequently used as an indicator of cellular signaling activity. Elevated phosphorylation of tyrosine kinase receptors plays an important role in cancer pathogenesis. However, phosphoproteins are usually poorly preserved in clinical tissue samples that are routinely fixed in 10% formalin. Nonetheless, in oncology clinical trials, use of phosphoproteins as biomarkers has been considered to be of great value in evaluating the effectiveness of a given drug candidate. Therefore, it is worthy of investigating whether alternative fixatives would improve the preservation of phosphoproteins in tissue. We compared the IHC staining of a number of phosphoproteins in xenograft and human surgical tumor tissues fixed in three different fixatives: 10% formalin, 4% paraformaldehyde (PFA), and Streck's tissue fixative (STF). We found that STF significantly enhanced the staining intensity of phosphoproteins compared with 10% formalin or 4% PFA. STF fixative also showed superiority of preservation of phosphoproteins in human surgical samples. Our results indicate that the choice of fixative could significantly affect the usability of clinical tissue samples for evaluating phosphoprotein by IHC.